The present invention generally relates to the area of electric heating elements. More particularly, the present invention relates to electric heating elements for use in heating residential and non-residential premises, specifically via construction panels and components such as walls and floors, etc., or different industrial or agricultural installations.
Previously known heating elements based on applying a thin metal coating to a resistor ribbon are disclosed in U.S. Pat. No. 4,839,500. The thin metal coating can be made of several different metals, such as tungsten, tantalum, molybdenum, titanium, or platinum. The coating can be formed by chemical processes including the following: vapor-phase deposition method, sputtering method, vapor deposition method (U.S. Pat. No.5,331,134). A number of patents also disclose the use of metal oxides in making the thin metal coating, e.g., a tin oxide coating (U.S. Pat. Nos. 4,889,974; 5,304,783; 5,616,266).
Other known types of heating elements are built using film printing technique as set forth in U.S. Pat. No. 5,068,517. The heating element is based on a silver-palladium alloy (AgPd) or a mixture of the silver-palladium alloy (AgPd) and ruthenium oxide (RuO2). The cover layer has a thickness of 10 mm. The heating elements of that type have relatively small overall dimensions. According to the patent specifications, the heating element is 270 mm long by 15-25 mm wide.
A number of problems are typically encountered in the practical use of such heating elements in heating installations. There is a need to use special subtle chemical technologies for applying a thin coating. It has been found particularly problematic to apply an even coating throughout the entire surface of the element. Moreover, such thin coatings have a short life. Also, the coatings are also made from expensive metals. In addition, the heaters thus manufactured are limited in size and power.
Another known type of heating device is based on a heating element made of metal foil as disclosed in U.S. Pat. No. 4,797,537; U.S. Pat. No. 4,889,973; EP 0227624 A1; EP 0175662 A1. All of these patents disclose metal foil-based heating devices manufactured by etching or punching. The etching method is applicable only in manufacturing heating elements of limited size. Heaters utilizing such elements are applicable, on the whole, in localized heating in determinate places. These heaters have good results for creating temperature zones of limited size within relatively small, confined spaces. Since the etching agent is not washed away after the etching process, the metal remains brittle and easily destructible, limiting the life-span of the heating element. Elements made using the punching method are similarly limited in size and can be used for small-capacity heaters only. Both methods also entail additional expenses with respect to heating material.
Another known type of heater utilizes a foil made of a highly conductive material, namely, aluminum (WO 9603013 A1, WO 05/22236, U.S. Pat. No. 4,574,186). The specific electric resistance of aluminum is lower than the specific resistance of the resistor alloy by a factor of 40 to 50. Therefore, the thickness of the foil is smaller (microns), and the foil is short lived.
A number of patents have been issued for methods of strengthening existing heating elements (U.S. Pat. No. 4,650,960), and of reinforcing them (U.S. Pat. No. 4,363,947) regardless of the technology used. The latter patent proposes a technology for strengthening a heating element (U.S. Pat. No. 4,025,863) by soldering reinforcing elements thereto. The problem, however, is that the use of a foil of lead-tin antimony alloy having a melting point of 180xc2x0 C. is proposed for the method in question. Lead, in addition to being an environmental pollutant, is very expensive.
All of the above described heating devices have a limited scope of practical application and a limited size and shape. In addition, the prior art heating devices are too complicated to make and require rare and expensive materials. Another problem is their limited lifespan.
The present invention, therefore, aims to allow the manufacture of more versatile two- and three-dimensional heating elements with larger effective heating surfaces (or practically unlimited shapes and sizes), with the added benefit of an increased life-span. All these goals can be attained using the proposed new electric heating element, intended for incorporation into different construction panels and materials for reliable electric heating.
An electric heating device in accordance with the present invention comprises a resistor ribbon, a plurality of sections of electroconductive coating attached to the resistor ribbon at preset intervals, and connector contacts coupled to the resistor ribbon for enabling connection of a power source to the resistor ribbon. Because of its thinness, the ribbon is naturally flexible.
Preferably, the flexible resistor ribbon has a high specific impedance. Also, where the flexible resistor ribbon has a width, each of the sections of the electroconductive coating are at least coextensive with the flexible resistor ribbon across the width thereof. It is generally contemplated that the sections of electroconductive coating, which are spaced from one another along the length of the ribbon, each have a length which is greater than the width of the ribbon. Thus, where the flexible resistor ribbon is folded back on itself at bend points located only at the sections of the electroconductive coating, the flexible resistor ribbon is mechanically reinforced at all the bend points by the sections of the electroconductive coating and electrical current is shunted across the bend points via the sections of the electroconductive coating, thereby eliminating overheating at the bend points.
The electroconductive coating of the spaced coating sections is generally the only layer of electroconductive coating which is applied to the resistor ribbon. The sections of coating in accordance with the present invention are spaced from each other by predetermined intervals or distances. These intervals or distances are determined by the expected use of the ribbon, and more particularly, by the expected locations of bending of the ribbon to conform to the size and shape of a preselected substrate.
The specific impedance of the resistor ribbon preferably adheres to the following formula R1/R2 greater than 2, where R1 is the specific impedance of the flexible resistor ribbon and R2 is a specific impedance of the electroconductive coating.
Where the heating device has a rated operational current Ielement and the electroconductive coating has a maximum admissible current Imax, a ratio between the rated operational current Ielement and the maximum admissible current Imax adhering to the formula:
Ielement/Imax less than {fraction (1/2.)}
In accordance with another feature of the present invention, the heating device further comprises a substrate, for example, a flat base to which the flexible resistor ribbon is attached. The base may be rigid or flexible and made of any of a variety of fire-resistant or fireproof materials including, without limitation, linoleum, PVC, plastic, fiberglass, or ceramic tile. In this form, the heating device is suitable for incorporation into a building as a floor, wall or ceiling panel.
Layers of electric insulation are advantageously attached to the base so as to sandwich the flexible resistor ribbon. Where the resistor ribbon is bent back on itself, for example, to form a snaking configuration, a strip of two-sided adhesive tape may be attached to the layers of electric insulation and to the ribbon at multiple spaced points in order to counteract differential thermal expansion of the various components of the heating device.
In a specific configuration of the heating device, a plate is connected to the base parallel thereto. The flexible resistor ribbon is mounted on a back side of the plate between the plate and the base. The heating device in that case also comprises layers of electric insulation attached to the base, the flexible resistor ribbon being disposed between the base and the layers of electric insulation.
In an alternative specific configuration of the heating device, a first layer of electric insulation is attached to a back side of the base. The flexible resistor ribbon is mounted on the first layer of electric insulation, while a second layer of electric insulation is positioned over the flexible resistor ribbon and the first layer of electric insulation. A metal casing is attached to the second layer of electric insulation and the base. A supplemental layer of insulation may be interposed between the second layer of electric insulation and the metal casing. In addition, the metal casing may incorporate connectors for operably connecting the metal casing to a power source. In that event, the metal casing and the connector means may comprise a seamless integral body. Where the metal casing incorporates a heat radiator, the metal casing and the heat radiator comprise a seamless integral body.
In another alternative specific configuration of the heating device, the base includes flexible electric insulation layers. The flexible electric insulation layers are selected from the group consisting essentially of plastic film and rubber sheeting.
In yet another alternative specific configuration of the heating device, the device further comprises an outer jacket or covering, the flexible resistor ribbon and the sections of the electroconductive coating being disposed inside the outer jacket or covering. The outer jacket or covering is preferably made of thermo-shrink plastic foil and is provided with external markings indicating bending sites at locations of the sections of the electroconductive coating.
In accordance with the present invention, a method for manufacturing an electric heating device utilizes a base having a sandwich assembly connected thereto. The sandwich assembly includes a first layer of electric insulation, a second layer of electric insulation and a resistor ribbon disposed therebetween, the sandwich assembly having a back side opposite the base. Pursuant to the inventive method, a thin electroconductive layer is applied to side edges of the base and the back side of the sandwich assembly. Then, the base together with the sandwich assembly and the electroconductive layer are electroplated to create a seamless metal casing attached to the base and the sandwich assembly.
The base with the sandwich assembly attached thereto may be manufactured by mounting the first layer of electric insulation to one side of the base, attaching the resistor ribbon to the first layer of electric insulation, and mounting the second layer of electric insulation to the first layer of electric insulation over the resistor ribbon.
In accordance with another feature of the present invention, the method of manufacture further includes the step of fitting an additional waterproof layer onto a back surface of the second layer of electric insulation. In that case, the waterproof layer is part of the sandwich assembly and the back side of the sandwich assembly is a surface of the waterproof layer. Then, the thin electroconductive layer is applied onto the surface of the waterproof layer.
The method of manufacture may further comprise the steps of applying a thick layer of a quick-melting, waterproof substance onto the sandwich assembly at a desired connection point of a power cable to the resistor ribbon, and sculpting the thick layer into a desired shape of a connector box. In this case, the thin electroconductive layer is applied also to the sculpted layer of the quick-melting, waterproof substance and the sculpted layer is also electroplated so that the seamless metal casing incorporates the connector box. In a subsequent step, the metal casing is heated to melt the quick-melting substance out of the metal casing to form the connector box.
Where the attaching of the resistor ribbon to the first layer of electric insulation includes bending the resistor ribbon at bend points, the resistor ribbon being provided with spaced sections of electroconductive reinforcement coating located at the bend points, the bending of the resistor ribbon includes bending the sections of the coating at the bend points.
A method of heating a building structure comprises, in accordance with the present invention, providing a flexible resistor ribbon mounted to an electric insulating material and to a building panel, mounting the panel to the building structure, and applying power to the flexible resistor ribbon to heat the panel and the building structure. The method may include mounting the flexible resistor ribbon to the electric insulating material and to the panel. The panel may be a wall panel or a floor panel.
An electric heating device comprises, in accordance with the present invention, a flexible resistor ribbon having high electrical impedance and including a first face mounted onto an insulated material and a second face mounted onto a substrate for direct heating thereof. The substrate may be ceramic, flexible or rigid plastic, leather or fabric. The second face of the ribbon may be wrapped around the substrate, woven into the substrate, molded into the substrate, or glued onto the substrate.
A heating device in accordance with the present invention facilitates the manufacture of more versatile two- and three-dimensional heaters with larger effective heating surfaces. The heating device permits the production of heaters of practically unlimited shapes and sizes. Life-span is increased over conventional heating devices incorporating resistor ribbons.
A heating element and particularly a resistive ribbon thereof in accordance with the present invention can be made of less expensive materials, for example, foil made from economically alloyed metal.
Heating devices in accordance with the invention may be manufactured easily via automation. The heating devices are versatile, reliable and cost-efficient.
Heating devices incorporating, in accordance with the present invention, a resistive ribbon with spaced electroconductive coating sections and a ceramic base with an external metal casing feature enhanced mechanical strength, fire and water resistance.
The present invention provides technical solutions which are innovative and capable of meeting the requirements for their application. The technical solutions are fit for industrial production, and as formulated in the present patent application, constitute a coherent invention.